So Now You Know

Caffeine doesn’t keep you awake by supplying extra energy; rather it fools your body into thinking it isn’t tired. When your brain is tired and wants to slow down, it releases a chemical called adenosine.

Adenosine travels to special cells called receptors, where it goes to work counteracting the chemicals that stimulate your brain. Caffeine mimics adenosine; so it can "plug up" your receptors and prevent adenosine from getting through. Result: Your brain never gets the signal to slow down, and keeps building up stimulants.